The purpose of these studies is to assess the effects of experimental long term pressure overload induced hypertrophy and failure on coronary perfusion in conscious dogs. The extent to which limitation of coronary vascular reserve can account for changes in ventricular function in the hypertrophied and failing heart at rest and during periods of cardiovascular stress (i.e., in response to severe, spontaneous exercise, short-term coronary artery occlusion and administration of potent coronary vasodilators) will be evaluated. Mongrel dogs will be instrumented with: miniature pressure gauges in the aorta and right ventricle; ultrasonic crystals for measurement of right ventricular segment length shortening and wall thickness; ultrasonic flow transducers and hydraulic occluders on the right main coronary artery; catheters in the right ventricle, left atrium and aorta; and hydraulic occluders on the pulmonary artery for the production of pressure overload hypertrophy and failure of the right ventricle. Alterations in the regional distribution of myocardial blood flow, as well as the development of coronary collateral circulation in hypertrophied and failing hearts will be measured by the radioactive microsphere technique. Moreover, changes in coronary flow and myocardial function in the presence of cardiac hypertrophy and failure will be examined in response to a) cardiovascular stress, e.g., exercise, coronary occlusion, adenosine, and b) neural stimuli, e.g., carotid occlusion and carotid chemoreceptor stimulation. The goal of these studies is to establish the manner in which the regulation of the coronary circulation is altered with the development of severe right ventricular hypertrophy and failure.